Referring to FIG. 1, a top view of a .mu.BGA (micro-Ball Grid Array) package 102 shows that the .mu.BGA package 102 holds an integrated circuit die 104. The .mu.BGA package 102 provides connection to nodes within the integrated circuit die 104 via bond pads on the integrated circuit die 104 to a solder ball of the .mu.BGA package 102. A .mu.BGA package includes an array of solder balls for providing connection to a plurality of nodes within the integrated circuit die 104. The .mu.BGA package 102 of FIG. 1 shows an array of just two rows by two columns of solder balls for clarity of illustration. However, a typical .mu.BGA package has an array of many more solder balls, as known to one of ordinary skill in the art of electronics.
Referring to FIG. 1, a first solder ball 106 of the .mu.BGA package 102 is coupled to a first bond pad 108 on the integrated circuit die 104. A first beam lead 110 is connected to the first bond pad 108, and a first metal interconnect 112 such as a copper interconnect is coupled between the first beam lead 110 and the first solder ball 106. Similarly, a second solder ball 114 of the .mu.BGA package 102 is coupled to a second bond pad 116 on the integrated circuit die 104. A second beam lead 118 is connected to the second bond pad 116, and a second metal interconnect 120 such as a copper interconnect is coupled between the second beam lead 118 and the second solder ball 114. In addition, a third solder ball 122 of the .mu.BGA package 102 is coupled to a third bond pad 124 on the integrated circuit die 104. A third beam lead 126 is connected to the third bond pad 124, and a third metal interconnect 128 such as a copper interconnect is coupled between the third beam lead 126 and the third solder ball 122. Furthermore, a fourth solder ball 130 of the .mu.BGA package 102 is coupled to a fourth bond pad 132 on the integrated circuit die 104. A fourth beam lead 134 is connected to the fourth bond pad 132, and a fourth metal interconnect 136 such as a copper interconnect is coupled between the fourth beam lead 134 and the fourth solder ball 130.
Referring to FIG. 2, a cross sectional view of an example beam lead and solder ball across the line A--A of FIG. 1 is shown. Elements having the same reference number in FIGS. 1 and 2 refer to elements having similar structure and function. The beam lead 134 forms an S-structure near the bond pad 132 of the integrated circuit die 104 to make contact with the bond pad 132. The copper interconnect 136 is deposited on the beam lead 134 to provide connection of the beam lead 134 to the solder ball 130. A polyimide material 150 is deposited on the copper interconnect 136 to encapsulate and protect the copper interconnect 136. Furthermore, a seal material 152, such as an elastomer seal, surrounds the beam lead 134 to encapsulate and protect the beam lead 134. A region of the .mu.BGA package 102 where each of at least one beam lead makes contact to a respective bond pad is referred to as an inner lead bond region 160 (shown within dashed lines in FIGS. 1 and 2).
Any integrated circuit package, including a .mu.BGA package, is tested for proper functionality of the integrated circuit die within that integrated circuit package. When the integrated circuit die within the integrated circuit package is not functioning properly, the mechanism causing the functional failure is determined through fault isolation techniques such that appropriate corrective measures may be taken to prevent such functional failure in other integrated circuit packages.
Referring to FIG. 2, the mechanism causing the functional failure of the integrated circuit die 104 within a .mu.BGA package may be due to faults within the inner lead bond region 160. For example, the beam lead 134 may not be properly connected to the bond pad 132 to result in an open circuit fault within the inner lead bond region 160. Because of the unique structural details within the inner lead bond region 160 of a .mu.BGA package, a fault isolation technique is desired for efficiently isolating any fault within the inner lead bond region 160 of the .mu.BGA package.
In addition, the mechanism causing the functional failure of the integrated circuit die 104 within a .mu.BGA package may be due to faults in areas of the .mu.BGA package outside of the inner lead bond region 160. Thus, the fault isolation technique for isolating any fault within the inner lead bond region 160 desirably preserves the structural integrity of the areas of the .mu.BGA package outside of the inner lead bond region 160 for later inspection of those areas.